Load range C and D tires including metallic cord belt layer of specified inch strength

ABSTRACT

Load Range C or D radial light truck tires have plies reinforced with metallic cords. At least one of the plies has an inch strength of at least 11,500 N/mm 2  per in. and is reinforced with 0.32 mm-0.40 mm filament diameter ultra tensile steel cords at 17-24 ends per inch. The ply may be located in any of the tire components such as the belt, carcass, chipper, or chafer.

This application is a divisional of U.S. application Ser. No.08/824,134, filed Mar. 27, 1997, now U.S. Pat. No. 6,293,326, issuedSep. 25, 2001. U.S. application Ser. No. 08/824, 134 is acontinuation-in-part of U.S. application Ser. No. 08/514,080 filed Aug.11, 1995, now abandoned, which is a division of U.S. application Ser.No. 08/360,973 filed Dec. 20, 1994, now abandoned. U.S. application Ser.No. 08/824, 134 is also a continuation-in-part of U.S. application Ser.No. 07/937,864 filed Oct. 13, 1992, now U.S. Pat. No. 5,616,197 and alsois a national stage application (371) of PCT/US91/01906, filed Mar. 21,1991, which is a continuation-in-part of U.S. application Ser. No.07/496,759 filed Mar. 21, 1990, now U.S. Statutory InventionRegistration H1333. The above applications are hereby incorporated byreference thereto.

This application is a Continuation-in-Part of two prior U.S.applications. The first is co-pending U.S. application Ser. No.08/514,080 filed Aug. 11, 1995, disclosing 2×0.35 ultra tensile cord forlight truck tires, and the second is a co-pending U.S. application Ser.No. 07/937,864 filed Oct. 13, 1992, which was a CIP of U.S. applicationSer. No. 07/496,759 filed Mar. 21, 1990, now a statutory inventionregistration number H-1333, the latter disclosing 2×0.255 super tensilecord and the former 2×0.30 super tensile cord. The above latter andformer applications are hereby incorporated by reference thereto.

FIELD OF THE INVENTION

The present invention relates to cord for tires and radial tires forvehicles, i.e., those tires wherein the cords of the carcass plies whichextend from one bead to the other lie substantially on radial planes.

Particularly, the present invention relates to light truck tires havingless weight favoring low-rolling resistance to absorb less horsepowerwhile maintaining the strength of the previous heavier construction aswell as ride and handling with a simpler construction cord of greatercorrosion resistance.

Assignees prior application, now published as EPO 237,462 on Sep. 16,1987, discloses a two-ply passenger tire belt having cords of 2×0.30high tensile construction. The high tensile material used was describedas high-carbon steel with a carbon content by weight of greater than0.80%.

Co-pending with this application is Assignees U.S. application Ser. No.07/843,133 filed Feb. 28, 1992, now abandoned disclosing 0.35 filamentsboth untwisted and twisted of super tensile material in a cord for areinforcement, particularly for radial medium truck tires.

BACKGROUND OF THE INVENTION

Assignees' previous light truck tires had a common cord, 2+2×0.30 hightensile for load range C and D tires, U.S. Pat. No. 5,188,685 issuedFeb. 23, 1993, and 2+2×0.35 ST for load range E tires, U.S. Pat. No.5,242,001 issued Sep. 7, 1993. The present invention using 2×0.35 cord,maintains a common 2× cord for these load ranges while taking the nextstep forward by reducing the number of filaments in the cord from fourto two. An alternate cord, 3×0.35 increases the number of filaments, butreduces the required tensile strength where the tensile strength for 2×cord would otherwise exceed what is available in current commercialmaterials. A key to efficient use of reinforcement is to use only asmuch as required by the product, but it is not always simply a matter ofincreasing a filament diameter to reach such a goal. Where the diameterincrease still results in an unobtainable tensile strength, a filamentmay have to be added, or the material changed, or the ends per inch ofcord changed, etc. To identify a specific type of cord for use over thewidest range of variables, including use of super tensile and ultratensile materials, it was found that the best way to illustrate thevariables was graphically as in FIG. 4 below where the preferredembodiment of 2× cord and an alternate embodiment of 3× cord show howthe variables for these cords can be brought together is illustrated.

SUMMARY OF THE INVENTION

Advantages which exist in the present cord over the previous cordinclude improved corrosion resistance and a weight reduction due toreduction in weight of reinforcement as well as reduction in the amountof total gum rubber gauge due to the smaller diameter of the presentcord, all of which result in a reduction in cost for the tire of thepresent invention. Further, the new belt structure using the presentcord is expected to give equal or better rolling resistance where it isrecognized that the belt, even though having a smaller diameter cord,has a higher bending stiffness for the belt structure.

This invention provides the above advantages in a load range C and Dpneumatic radial tire with a carcass having radial cords and twosidewalls spaced apart a distance which, in the axial direction,determines the width of the tire section. The tire has two beads eachone of which around which are turned up, from the inside toward theoutside, the ends of the cords of the carcass. A tread is disposed onthe crown of the carcass, and a belt structure that is circumferentiallyinextensible is interposed between the tread and the carcass. The beltstructure has a width that is substantially equal to that of the treadand has two radially overlapped layers of elastomeric fabric reinforcedwith metallic cords. The metallic cords are parallel to each other ineach layer, which layers have a density of 28 ends per inch with afilament tensile strength of at least 3500 MPa and a 032 mm filamentdiameter. The cords of one layer are crossed with the other layer andinclined at an angle of between 16° and 30° with respect to theequatorial plane of the tire. The metallic cords being two singlefilaments twisted one about the other.

Further, this invention provides a pneumatic radial tire with a carcasshaving radial cords, two sidewalls spaced apart a distance, which in theaxial direction, determines the width of the tire section, two beadseach one of which around which are turned up the ends of the cords ofthe carcass, and a belt structure that is circumferentially inextensibleinterposed between the tread and the carcass, the belt structure havinga width that is substantially equal to that of the tread and having atleast two radially overlapped layers of elastomeric fabric reinforcedwith metallic cords, the metallic cords being parallel to each other ineach layer, comprising at least one layer of cords comprising twofilaments twisted about each other having a diameter of about 032 mm to0.40 mm and a filament tensile strength (T) of at least T=6908-10740 (d)for a Load Range D tire.

Lastly, this invention provides a pneumatic tire with a carcass havingradial cords, two sidewalls spaced apart a distance, which in the axialdirection, determines the width of the tire section, two beads each oneof which around which are turned up the ends of the cords of thecarcass, and a belt structure that is circumferentially inextensibleinterposed between the tread and the carcass, the belt structure havinga width that is substantially equal to that of the tread and having atleast two radially overlapped layers of elastomeric fabric reinforcedwith metallic cords, the metallic cords being parallel to each other ineach layer, comprising at least one layer of an inch strength (In.Str.)of at least 11,500 N/mm² per in. for Load Range C wherein:

In.Str. (Newtons/mm² per inch)=N{CE(C-2000 Newtons/mm³·d)}EPI

N=number of filaments per cord=2[OR MORE] or more

d=filament diameter=0.32 to 0.40 mm

CE=Cord Efficiency

EPI=cord end count=17 to 19 ends/inch

C=4080 to 4400 Newtons/nm²

while for Load Range C and D the In.Str. would be at least 14,500 N/mm²per in. and the ranges for EPI, 17-24 and C=4080 to 4400.

In further aspects of the present invention, the filament diameters ofboth filaments in the cord are 0.35 mm diameter and the ends per inchare 17 with ultra tensile and 19 with super tensile material for loadrange C tires and 21 ends per inch for ultra tensile and 24 ends perinch for super tensile for load range D tires.

The features of the present invention, which are believed to be novel,are set forth with particularity in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention, both as to its structure and manner of operation,may best be understood by reference to the following detaileddescription, taken in accordance with the accompanying drawings inwhich:

FIG. 1 is a cross-sectional view of a tire in a plane that contains theaxis of rotation of the tire and in accordance with the presentinvention;

FIG. 2 is an enlarged schematic of the annular reinforcing portion ofthe tire shown in FIG. 1;

FIG. 3 is an enlarged cross-sectional view of a cord from thereinforcing portion of the tire in FIG. 2; and

FIG. 4 is a graph illustrating tensile strength of cord filament inrelation to filament diameter.

DEFINITIONS

As used herein and in the claims:

“Axial” and “axially” are used herein to refer to lines or directionsthat are parallel to the axis of rotation of the tire.

“Bead” means that part of the tire comprising an annular tensile memberwrapped by ply cords and shaped, with or without other reinforcementelements such as flippers, chippers, apexes, toeguards and chafers, tofit the design rim.

“Belt structure” means at least two layers or plies of parallel cords,woven or unwoven, underlying the tread, unanchored to the bead, andhaving both left and right cord angles in the range from 16 degrees to30 degrees with respect to the equatorial plane of the tire.

“Carcass” means the tire structure apart from the belt structure, tread,undertread, and sidewall rubber over the plies, but including the beads.

“Cord” means one or more of the reinforcement elements, formed by one ormore filaments/wires which may or may not be twisted or otherwise formedwhich may further include strands so formed which strands may or may notbe also so formed, of which the plies in the tire are comprised.

“Crown” means that portion of the tire within the width limits of thetire tread.

“Density” means quantity per unit length.

“Equatorial plane (EP)” means the plane perpendicular to the tire's axisof rotation and passing through the center of its tread.

“Gauge” means material thickness.

“High Tensile Steel (HT)” means a carbon steel with at least 0.80%carbon by weight, or a tensile strength of at least 3240 MPa at 0.30 mmfilament diameter.

“Super Tensile Steel (ST)” means a carbon steel with a content by weightof between 0.78% and 0.86% carbon, 0.3% to 1.0% Si and between 0.1% and0.5% of an alloying element from a class of the following elements: Cr,Ni, Co, W, V and Nb, and any combination thereof, the balance being ironand residuals, or a tensile strength of at least 3380 MPa at 0.35 mmfilament diameter.

“Ultra Tensile Steel (UT)” means a steel as disclosed in U.S. Pat. No.6,099,797 issued Aug. 8, 2000 and hereby incorporated by referringthereto or carbon steel with a tensile strength of at least 3700 MPa at0.35 mm filament diameter.

“Load Range C and D” means load and inflation limits for a given tireused in a specific type of service as defined by tables in The Tire andRim Association, Inc., 1989 Year Book.

“Radial” and “radially” are used to mean directions radially toward oraway from the axis of rotation of the tire.

“Section width” means the maximum linear distance parallel to the axisof the tire and between the exterior of its sidewalls when and after ithas been inflated at normal pressure for 24 hours, unloaded, excludingelevations of the sidewalls due to labeling, decoration or protectivebands.

“Stiffness Ratio” means the value of the control belt structurestiffness divided into the value of another belt structure when thevalues are determined by a fixed three (3) point bending test havingboth ends of the cord fixed and flexed by a load centered between thefixed ends.

“Tread” means that portion of a tire that comes into contact with theroad when the tire is normally inflated and under normal load.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 to 3, there is illustrated, by means of a workingexample, a tire of size LT225/75R16 for load ranges C and D. For thepreferred embodiments illustrated herein all actual dimensions giventherein are for a tire of the above size. A pneumatic tire 10 accordingto the invention has what is commonly referred to in the tire art as aradial ply carcass structure. For the purposes of the present invention,a tire has a radial ply carcass structure when the cords of the carcassreinforcing ply, or plies 11, 12, are oriented at angles in the range of75° to 90° with respect to the equatorial plane (EP) of the tire.

The tire 10 according to the invention has a pair of substantiallyinextensible annular beads 13, 14 which are axially spaced apart fromone another. Each of the beads 13, 14 is located in a bead portion ofthe tire which has exterior surfaces configured to be complimentary tothe bead seats and retaining flanges of a rim (not shown) upon which thetire is designed to be mounted. A radial ply carcass structure, in thepreferred embodiment comprising two plies 11, 12 of side-by-sidereinforced cords of polyester material, extends between the beads withan axially outer portion of the carcass structure folded about each ofthe beads. While in the preferred embodiment, the carcass ply structurecomprises two plies of reinforcing material, it is understood that oneor more carcass plies of any suitable material may be employed withoutdeviating from the scope of the present invention.

Preferably, a tire according to the invention is a tubeless tire havinga layer of a low permeability material 9 disposed inwardly of thecarcass plies 11, 12 and contiguous to an inflation chamber defined bythe tire and rim assembly. Elastomeric sidewalls 15, 16 are disposedaxially outwardly of the carcass structure. A circumferentiallyextending belt structure 17 comprising two layers 18, 20 (FIG. 2), eachof which preferably comprises steel reinforcing cords 22 (FIG. 3)characterized by the cords 22 having filaments 24, 26 with a breakingstrength of at least 3380 MPa at 0.35 mm filament diameter. Each cord 22has two filaments 24, 26 twisted together with a 16 mm lay length. Thiscord is designated as 2× and is known for its openness and good rubberpenetration resulting from the openness.

More particularly, load range C tires are built with two belts asillustrated in FIG. 2 with alternately 2×0.35 super tensile cords at 19ends per inch or 2×0.35 ultra tensile cords at 17 ends per inch with theangle θ of one ply being approximately 21° and the other ply having anidentical but opposing angle. Load range D tires were built with twobelts as illustrated in FIG. 2 with alternately 2×0.35 super tensilecord at 24 ends per inch or 2×0.35 ultra tensile cord at 21 ends perinch with the same cord angle θ and ply construction as described abovefor load range C tires. It is anticipated that metallic cord density inthe belt layers from 13 to 28 ends per inch will be useful for loadranges C and D tires with the filament diameter ranging from 0.32 to0.40 mm. Tires of the above preferred embodiments are presently undertests and anticipated to give equal or better results to the controltire of 2+2×0.30 high tensile cord construction.

Tables 1 and 2 below compare the control (2+2×0.30 high tensile) cord tothat of the present invention.

TABLE I 2X.35 STEEL CORD FOR RLT BELTS 2 + 2X.30 HT (CONTROL) 2X.35 ST2X.35 UT LR-C TIRES EPI 13 19 17 Steel Cord Weight (lbs/tire) 2.12 2.121.90 Compound Weight (lbs/tire) 2.64 2.42 2.47 Treatment Weight(lbs/tire) 4.77 4.54 4.37 Weight Savings (lbs/tire) 0.23 0.40 LR-D TIRESEPI 17 24 21 Steel Cord Weight (lbs/tire) 2.69 2.60 2.28 Compound Weight(lbs/tire) 2.41 2.25 2.31 Treatment Weight (lbs/tire) 5.10 4.85 4.59Weight Savings (lbs/tire) 0.25 0.51

TABLE II 2X.35 STEEL CORD FOR RLT BELTS 2 + 2X.30HT 13 EPI 17 EPI2X.35ST 2X.35UT (CONTROL) 19 EPI 24 EPI 17 EPI 22 EPI Tire ApplicationLR-C LR-D C D C D Steel Cord Properties Breaking Strength (N) 890 890618 618 680 680 Maximum Gauge (mm) 0.90 0.90 0.70 0.70 0.70 0.70 BendingStiffness 324 324 300 300 300 300 Layer Properties EPI 13 17 19 24 17 21Rivet (inch) .042 .023 .025 .014 .031 .020 Inch-Strength (N/in) 1160015100 11700 14800 11600 14300 Inch-Stiffness 4200 5500 5700 7200 51006300

For both load ranges C and D, Table I illustrates a weight savings ofthe present cord over Control and, further, in both instances, the ultratensile cords provide greater savings over even the super tensile cordconstructions. These weight savings also will result in cost savings inthe tires as well.

In Table II, the cord properties are first compared to Control and areseen to be below the strength limitations and stiffness of the Controlcord, however, when the properties of the layer which the present cordsform is compared to the layer formed by the Control cord, it can be seenthat the inch strength and inch stiffness of the present layer exceedsthat of the Control layer even though the cord properties are below thatof the Control cord. While as is noted above testing is ongoing, it isanticipated that the increased strength and stiffness may well result inhigher rolling resistance; but in any case, it is anticipated that atleast equal performance to Control will be achieved.

The weight savings are from a reduction in not only the weight of thereinforcing cord, but also from a reduction in the treatment gaugeneeded to encapsulate the reinforcing cord. Turning to FIG. 2, it can beappreciated that if the treatment gauge decreases with cord diameter(d), then gum between the cord will be reduced as well. The gum gauge(g) can remain constant with changing cord diameter. For example, if thecord diameter is the smallest surrounding circle around the maximumcross-section height of the cord, the load range C & D previous cord of2+2×0.30 high tensile has a cord diameter of 0.035 inches, while the2×0.35 super and ultra tensile cords of the present invention have adiameter of 0.028 inches. As a result, with a treatment gauge of 0.056inches for the 2+2×0.30 high tensile cord, and maintaining an equal gumgauge (g), the treatment gauge of the 2×0.35 super and ultra tensilecords of the present invention would be 0.048 inches, a 14% reduction.The above reduction made production of reinforcement for tires in loadranges C and D more economical. The identification of a common cord andrecognition of dual strength ranges is exemplified by the chart in FIG.4 which illustrates the preferred embodiment 2×0.35 cord together withalternate 3×0.35 cord. This chart was developed using the minimum andmaximum rivets for both cords and the required inch strength for LoadRange C and D tires. The upper range of 2× cord construction is definedby line a, and the expression T=14238-25590 (d), and the lower limit bythe line C and the expression T=6908-10740 (d). Similarly, for 3× cord,the upper dashed line b has the expression T=9616-17370 (d) and thelower dashed line e the expression T=4998-8140 (d). Similar lines can bedeveloped for other similar type cords.

The chart shows the relationship between filament tensile strength inMPa plotted on the vertical axis, and the filament diameter in mmplotted on the horizontal axis.

Ideally, the cord is chosen to be close to the bottom line for bettereconomy, less weight and better rolling resistance, etc. For example,for 2× cord of 0.35 mm diameter, the use of super tensile material givesa value of T=3380 MPa, which is just above the line, see the asterisk,while if ultra tensile material were used, the value for T would be 3700MPa, see the circle, which is more conservative. On the other hand, ifsuper tensile material was used with 2× cord at 032 mm, its value of3440 MPa can be seen at X to be inadequate while ultra tensile with itsvalue of 3760 MPa would be adequate.

What has been demonstrated is a type cord construction for use inpneumatic radial tires, particularly light truck tires, but useful forany ply of a tire, such as carcass, or component i.e. chipper, chaffer,etc.

In accordance with the provisions of the patent statutes, the principaland mode of operation of the tires have been explained in what isconsidered to be their best embodiment have been illustrated anddescribed. It should, however, be understood that the invention may bepracticed otherwise than as specifically illustrated and describedwithout departing from its spirit and scope.

We claim:
 1. A Load Range C or D pneumatic radial tire with a carcass having radial cords, two sidewalls spaced apart a distance, which in the axial direction, determines the width of the tire section, two beads each one of which around which are turned up the ends of the cords of the carcass, a tread radially outward of the carcass, and a belt structure that is circumferentially inextensible interposed between the tread and the carcass, the belt structure having a width that is substantially equal to that of the tread and having two radially overlapped layers of elastomeric fabric reinforced with metallic cords, the metallic cords being parallel to each other in each layer, comprising at least one of said two radially overlapped layers having an inch strength (In.Str.) of at least 11,500 N/mm² per in. wherein: In.Str. (Newtons/mm² per inch)=N{CE(C-2000 Newtons/mm³·d)}EPI N=number of filaments per cord=2[OR MORE] or more d=filament diameter=0.32 to 0.40 mm CE=Cord Efficiency EPI=cord end count=17 to 24 ends/inch C=4080 to 4400 Newtons/mm².
 2. THE tire of claim 1 wherein d=0.35 mm and N=2.
 3. The tire of claim 2 wherein EPI=17 ends/inch and C=4400 Newtons/mm².
 4. The tire of claim 1 wherein the tire is Load Range D, In.Str.=at least 14,500 N/mm² per in., and EPI=21 to 24 ends/inch.
 5. The tire of claim 4 wherein d=0.35 mm and N=2.
 6. The tire of claim 5 wherein EPI=24 ends/inch and C=4080 N/mm². 